Vue Pinia's function is undefined in onMounted when running unit tests

Question

I have a component and a Pinia store that contains state and some operations. The code runs perfectly fine in browser and E2E (cypress) tests, but fails in unit tests. I'm using vue-testing-utils and vitest.

Calling a stored function from a unit test works fine when a button is clicked, but if the function is in an installed or main script, the test fails

src/components/UsersComponent.vue

<script setup>
import { onMounted } from 'vue'
import { useUsersStore } from '@/stores/users.store'

const usersStore = useUsersStore()
// usersStore.resetStatus() // <- This fails in the unit test

onMounted(() => {
  usersStore.resetStatus() // <- This fails in the unit test
})

function changeStatus() {
  usersStore.changeStatus() // <- This passes in the unit test
}
</script>

<template>
  <div>
    <p>Status: {{ usersStore.status }}</p>
    <button @click="changeStatus()">Change Status</button>
  </div>
</template>

src/stores/users.store.js

import { defineStore } from 'pinia'
import { usersAPI } from '@/gateways'

export const useUsersStore  = defineStore({
  id: 'users',
  persist: true,

  state: () => ({
    status: 'ready',
  }),

  getters: {},

  actions: {
    resetStatus() {
      this.status = 'ready'
    },
    changeStatus() {
      this.status = 'loading'
    },
  },
})

src/components/Test/UsersComponent.spec.js

import { describe, it, expect, vi, beforeEach } from 'vitest'
import { mount } from '@vue/test-utils'
import { createTestingPinia } from '@pinia/testing'

import UsersComponent from '@/components/UsersComponent.vue'
import { useUsersStore } from '@/stores/users.store'

const wrapper = mount(UsersComponent, {
  global: {
    plugins: [createTestingPinia({ createSpy: vi.fn() })],
  },
})
const usersStore = useUsersStore()

describe('UsersComponent', () => {
  it('store function is called', async () => {
    // arrange
    const spy = vi.spyOn(usersStore, 'resetStatus')
    const button = wrapper.find('button')

    // act
    await button.trigger('click')

    // assert
    expect(spy).toHaveBeenCalled()
  })
})

Unit test returns 2 different errors. The first is the console log when the function tries to run in onMounted() and the second is what vitest returns.

stderr | unknown test
[Vue warn]: Unhandled error during execution of mounted hook 
  at <UsersComponent ref="VTU_COMPONENT" >
  at <VTUROOT>

FAIL  src/components/__tests__/UsersComponent.spec.js [ src/components/__tests__/UsersComponent.spec.js ]
TypeError: usersStore.resetStatus is not a function
 ❯ src/components/UsersComponent.vue:16:14
     16|
     17| <template>
     18|   <div>
       |  ^
     19|     <p>Status: {{ usersStore.status }}</p>
     20|     <button @click="changeStatus()">Change Status</button>

I know this example is a bit basic and doesn't really serve the purpose, but I'd like to know how to have a stored function in onMounted() (or somewhere similar) without breaking all my unit tests .

Answer 1

Maybe this will work for you:

describe('UsersComponent',  () => {
  it('changeStatus function is called', async () => {
    const wrapper = mount(UsersComponent, {
      mounted: vi.fn(), // With this you mock the onMounted
      global: {
        plugins: [createTestingPinia({
          initialState: { // Initialize the state
            users: { status: 'ready' }, 
          }
        })]
      }
    })  
  
    // Spy the method you call...
    const spy = vi.spyOn(wrapper.vm, 'changeStatus');

    wrapper.vm.changeStatus()

    expect(spy).toHaveBeenCalled()
    expect(spy).toHaveBeenCalledTimes(1)
  })
})